DNA’s Discovery and
Structure

Scientists that determined DNA’s
Structure and Importance


1866 Gregor Mendel – demonstrated that parents pass traits to offspring-thought traits contained in a molecule
1869 Friedrich Meisher – Isolated DNA from cell nucleus – named it nucleic acid
 1889 R.A. Altman-determined the chemical composition of DNA

Scientists that Determined DNA’s
Structure and Importance
 1919 Phoebus Levene – Determined the structure of a DNA nucleotide
– first to propose that DNA was a polymer made of nucleotides
P = Phosphate S= 5C sugar B= Nitrogen base

Scientists that Determined DNA’s
Structure and Importance
 @1928 Frederick Griffith – bacterial transformation – traits passed by a chemical
“transforming principle”@

Scientists that Determined
DNA’s Structure and
Importance
 1944 Oswald Avery – DNA = key to transformation
- Avery and his partners conducted experiments which proved that DNA was Griffith’s
“transforming principle”

Scientists that Determined DNA’s
Structure and Importance
 1949 Erwin Chargaff – base-pairing rules
%Adenine=%Thymine %Guanine=%Cytosine
 1952 Alfred Hershey & Martha Chase
– Radioactive labeled Bacteriophage transformation experiment-settled
DNA-protein debate

Hershey & Chase

Important Scientists in the “Race for the Double Helix”
 1952 Maurice Wilkins & Rosalind Franklin
– X-ray diffraction“photographs” of DNA
–
–
DNA must be a some type of spiral (helix)
DNA’s diameter is constant and stable

Important Scientists in the “Race for the Double Helix”
 1953 James Watson & Francis Crick
– @Created the first accurate 3-D model of
DNA@
– Won the Nobel Prize with Wilkins

DNA’s Structure
 DNA is composed of nucleotides
 DNA contains four nitrogen bases: adenine(A) cytosine(C) guanine(G) thymine (T)
 @A & G are purines C & T are pyrimidines@

DNA’s Structure
 DNA is a double helix
-2 strands of DNA nucleotides joined to form a
“twisted ladder”
-the strands are held by hydrogen bonds between the nitrogen bases

Chargaff’s Rule

The nitrogen bases form the “steps” on the
DNA ladder by complementary pairing
A == T
C
T
==
==
G
A
Sugarphosphate backbone
G == C
A == T @ A always pairs with T
T == A C always pairs with G@

How the Code Works
 The combination of A,T,G,C determines what traits you might have..
 C A T C A T = purple hair
 T A C T A C = yellow hair

How the Code Works
 Think of the bases of DNA like letters

Letters form words…
 Words form sentences..

Central Dogma of Molecular
Biology
 1958 Francis Crick proposed:
@ DNA codes for the production of RNA
RNA codes for the production of protein@
Protein does not code for the production of protein DNA or RNA
“Once information has passed into protein it cannot get back out again”

Who discovered the bacterial transformation?
A.
B.
C.
D.
Watson and Crick
Wilkins and Franklin
Griffith
Avery

Who created the first 3D model of the double helix DNA?
A.
B.
C.
D.
Watson and Crick
Wilkins and Franklin
Griffith
Avery

What is the complementary strand to C G T A
 G C A T